WO 2004/053035 discloses a device in the form of a centrifugal separator for purifying an oil from particles. For the purification of the oil, a separation aid which binds the particles is added and thereby increases the degree of separation compared with using only the rotation of the rotor.
A problem with the purifying of oil according to the prior art is that some of the particles separated from the oil deposit themselves, together with separation aid, on the inside of the rotor in the form of a highly viscous layer of separated particles and separation aid. This layer of separated particles constitutes a relatively solid sludge phase which grows radially inwards towards the axis of rotation, impairing the degree of separation and ultimately rendering continued separation impossible because of obstruction.